A curable composition has been improved in various ways taking account of the application, and is widely used as a raw material, an adhesive, a coating material, and the like that are used to produce optical parts and formed articles.
A curable composition also has attracted attention as an optical element-securing composition (e.g., optical element adhesive and optical element sealing material) that is used when producing a sealed optical element.
Examples of the optical element include a light-emitting element (e.g., laser (e.g., semiconductor laser diode (LD)) and light-emitting diode (LED)), a light-receiving element, a hybrid optical element, an optical integrated circuit, and the like.
In recent years, an optical element that emits blue light or white light (i.e., an optical element that has a shorter emission peak wavelength) has been developed, and is widely used. There has been a tendency that an optical element having a short emission peak wavelength generates a larger amount of heat along with a rapid increase in brightness.
Along with a recent increase in the brightness of an optical element, a cured product of an optical element-securing composition may deteriorate due to long-term exposure to high-energy light or high-temperature heat generated by such an optical element, whereby delamination or a decrease in adhesion may occur.
In order to solve the above problem, Patent Literature 1 to 3 propose an optical element-securing composition that includes a polysilsesquioxane compound as the main component, and Patent Literature 4 proposes a semiconductor light-emitting device member and the like that utilize a hydrolysis-polycondensation product of a silane compound.
However, the compositions and the cured product (e.g., member) disclosed in Patent Literature 1 to 4 may not exhibit sufficient delamination resistance and heat resistance while maintaining sufficient adhesion.
A coating (application) device having a discharge tube (needle) (see Patent Literature 5) is normally used to apply a curable composition in order to secure an optical element or the like. Such a coating device having a discharge tube is designed so that the discharge tube moves vertically downward to approach the coating target, discharges a specific amount of curable composition from the end thereof, and moves upward so as to move away from the coating target while the coating target moves sideways. The curable composition can be continuously and efficiently applied by repeating this operation.
However, when a curable composition having high viscosity is used, for example, the curable composition that has been discharged from the discharge tube may not break, and may string (i.e., stringing phenomenon) when the discharge tube moves upward. If the coating target moves sideways in a state in which the curable composition has stringed, the curable composition may adhere to the coating target in an area other than the intended application target area (i.e., resin paste bridge may occur), whereby the coating target may be contaminated.
This problem can be solved by decreasing the viscosity of the curable composition. In this case, however, since the curable composition that has been discharged easily spreads, the coating target may be contaminated.
Therefore, development of a curable composition that produces a cured product that exhibits excellent adhesion, excellent delamination resistance, and excellent heat resistance, and can be continuously (successively) applied without contaminating the coating target (i.e., exhibits excellent workability during the application step), has been desired.